Hibernate foreign key with a part of composite pri

问题:

I have to work with Hibernate and I am not very sure how to solve this problem, I have 2 tables with a 1..n relationship like this:

-------
TABLE_A
-------
col_b (pk)
col_c (pk)
[other fields]

-------
TABLE_B
-------
col_a (pk)
col_b (pk) (fk TABLE_A.col_b)
col_c (fk TABLE_A.col_c)
[other fields]

How can I manage this with Hibernate?

I do not have any idea how to declare a foreign key that would contain a part of primary key.

My database schema is generated from the Hibernate model.

回答1:

I have found two solutions to this problem.

The first one is rather a workaround and is not so neat as the second one.

Define the primary key of the B entity as composite key containing col_a, col_b, and col_c and what was supposed to be the primary key in the first place, define as unique constraint. The disadvantage is that the column col_c is not really conceptually a part of primary key.

@Entity
class A {
  @Id
  private int b;
  @Id
  private int c;
}

@Entity
@Table(uniqueConstraints = {@UniqueConstraint(columnNames = { "a", "b" }) })
class B {
  @Id
  private int a;

  @Id
  @ManyToOne(optional = false)
  @JoinColumns(value = {
          @JoinColumn(name = "b", referencedColumnName = "b"),
          @JoinColumn(name = "c", referencedColumnName = "c") })
  private A entityA;
}

The second uses @EmbeddedId and @MapsId annotations and does exactly what I wanted to be done at the very beginning.

@Entity
class A {
  @Id
  private int b;
  @Id
  private int c;
}

@Embeddable
class BKey {
  private int a;
  private int b;
}

@Entity
class B {
  @EmbeddedId
  private BKey primaryKey;

  @MapsId("b")
  @ManyToOne(optional = false)
  @JoinColumns(value = {
          @JoinColumn(name = "b", referencedColumnName = "b"),
          @JoinColumn(name = "c", referencedColumnName = "c") })
  private A entityA;
}

回答2:

Jagger's second solution that is my first reaction, with @EmbededId and @MapsId. The following is another way based on his second solution but without using @MapsId. `

@Entity
class A {
  @Id
  private int b;
  @Id
  private int c;
}

@Embeddable
class BKey {
  private int a;
  private int b;
}

@Entity
class B {
  @EmbeddedId
  private BKey primaryKey;

  @ManyToOne(optional = false)
  @JoinColumns(value = {
          @JoinColumn(name = "b", referencedColumnName = "b", insertable= false, updatable= false),
          @JoinColumn(name = "c", referencedColumnName = "c") }, )
  private A entityA;
}